1. Field of the Invention
The present invention relates to an ignition coil. More specifically, the present invention relates to an ignition coil which is utilized for applying a high voltage pulse to an ignition plug of an automobile.
2. Description of the Prior Art
As shown in FIG. 11, in a conventional ignition coil 1, a primary coil 3 and a secondary coil 4 each being consist of an insulated copper wire are wound on a core 2, and a capacitor 5 is connected in parallel to the primary coil 3. Each of the primary coil 3 and the capacitor 5 is a lumped element, and a thyristor 6 is inserted between the both. Then, a damper diode 7 is connected in parallel to the primary coil 3. An input of such an ignition coil 1 is supplied with a direct current high voltage which is obtained by stepping a voltage of 12 V or 24 V of direct current from a battery up to 300-500 V of a direct current voltage by means of a DC--DC converter. The capacitor 5 is charged by the direct current high voltage. Then, by turning the thyristor 6 on, a discharging current flows from the capacitor 5 to the primary coil 3, and therefore, a voltage is induced on the secondary coil 4.
In such the ignition coil 1, the voltage induced on the secondary coil 4 becomes a sine wave-form as shown in FIG. 12. Actually, since a negative polarity side of the voltage indicated by a dotted line 8 is clamped by the damper diode 7, the voltage of the secondary coil 4 shows a wave-form having a single peak as shown by a solid line 9. Since this secondary voltage rises slowly and it takes time until the voltage reaches the peak, firing of the ignition plug is delayed and thus combustion efficiency is not good.